Polyamide resin is characterized by excellent mechanical properties, mold-processability and chemical resistance and therefore, is being widely used for automobile parts, electronic/electrical parts, mechanical parts, building materials, housing facility-related parts and the like. However, polyamide resin is extremely susceptible to oxidation deterioration and, accompanying a decrease in the polymerization degree, undesired phenomenan occur, such as reduction in mechanical strength, and generation of cracks and coloring on the surface. This oxidation deterioration is accelerated particularly by heat or light. Therefore, use of the polyamide resin is limited outdoors.
For the purpose of preventing such deterioration phenomena, a technique of adding various stabilizers to the polyamide resin is disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 48-93652 and 2-229853. However, their effect of improving the weather resistance is not satisfactory.
On the other hand, Japanese Examined Patent Publication (Kokoku) No. 7-103330 discloses a polyamide resin composition, improved in weather resistance, in which a hindered phenol-base heat-resistant agent, a triazole-base ultraviolet absorber and a hindered amine-base light-resistant stabilizer are blended to a specific polyamide. Japanese Unexamined Patent Publication No. 5-93134 discloses a weather-resistant composition in which a triazole-base ultraviolet absorber, a hindered amine-base light-resistant stabilizer, an alkali metal halide salt and a copper iodide are blended with a specific polyamide. Japanese Unexamined Patent Publication (Kokai) No. 10-182874 discloses a long-life weather-resistant polymer resin composition comprising polyamide 11 and/or polyamide 12, a hindered phenol heat resistant agent, a phosphorus-base working stabilizer, a triazole ultraviolet absorber, and low molecular weight and high molecular weight hindered amine light resistant agents.
In these methods, the weather resistance is improved by using an ultraviolet absorber (UVA) and a hindered amine-base light-resistant stabilizer in combination. However, when the polyamide resin composition contains a metal component, for example, in the case of a color grade polyamide resin composition using a pigment containing a metal component such as titanium oxide, or a polyamide resin composition containing a residual catalyst from the polymerization of resin, the metal component reacts with a UVA to form a complex and therefore, the synergistic effect for light resistance of UVA cannot be obtained. Thus, use of these methods is limited.
The object of the present invention is to solve the above-described problems and provide a polyamide resin composition capable of sufficiently exerting high weather resistance even when the polyamide resin contains a pigment containing a metal component such as titanium oxide, or a residual catalyst containing a metal component.